Recently, the development of a technology for presenting stereoscopic video has made progress, and head mount displays (Head Mounted Display; hereinafter described as an “HMD”) capable of presenting stereoscopic video having a depth have spread. Such HMDs include an optically transmissive HMD that has been developed which enables a user to view a state of the outside of the HMD in a see-through manner while presenting stereoscopic video to the user using a holographic element, a half-silvered mirror, and the like.
In addition, the performance of television monitors has been improved, and three-dimensional monitors capable of presenting stereoscopic video having a depth have spread. Unlike monitors that display conventional two-dimensional video, the video presented by a three-dimensional monitor is a stereoscopic video having a depth in a frontward-rearward direction. There are various systems as technologies for realizing such a three-dimensional monitor. An example thereof is a three-dimensional monitor of a frame sequential system that displays a parallax image for a left eye and a parallax image for a right eye alternately on a time-division basis. A user can observe stereoscopic video by observing the video through shutter eyeglasses having shutters opened and closed in synchronism with the display of the three-dimensional monitor of the frame sequential system.
The inventor of the present application has come to realize a possibility of providing an optically transmissive HMD with optical shutters for observing a three-dimensional monitor of the frame sequential system, and thereby presenting stereoscopic video by both of the three-dimensional monitor and the HMD. The inventor of the present application has also come to realize a possibility of adjusting an amount of external light incident on the optically transmissive HMD by using the optical shutters even when the three-dimensional monitor is not observed, and thus improving the visibility of video on the HMD.